Cannot set up vending machine offers

Hi,
I am not sure if I am doing something wrong here, but I cannot get the plugin to work.
Plugin is loaded and I followed the "guide" on the description page but regardless of which item I choose to set up to be sold I constantly get message "Invalid stack size. Please enter a valid number."

When I stand in front of a VM, I type /vm in chat.
Then hold the item I want to sell, open chat and type any number which results in above mentioned error message.
Screenshot is attached.
I am using Stack Modifier if that is relevant here.

Any help here is appreciated.

EDIT: tested on a test server where it worked. Trying to narrow down if another plugin interferes.

What value are you typing in for you stack size?

The values don't matter, I tried the same on another live server as well as a test server.
There it works. Tried from 1 - 500, on this specific server it won't work. 
Currently loading in the plugins manually to see which one would interfere.

11 minutes ago, INFINITY-Z said:

The values don't matter, I tried the same on another live server as well as a test server.
There it works. Tried from 1 - 500, on this specific server it won't work. 
Currently loading in the plugins manually to see which one would interfere.

The reason I was asking value is I didn’t know if you were using commas and they would cause that error to occur. 

I see, however I only used full values. I will get back if I find out more.

35 minutes ago, INFINITY-Z said:

I see, however I only used full values. I will get back if I find out more.

I would like to add you on discord so I can send you a copy of it with a debug console message. It will display what the plugin is trying to interpret as the stack size value. This could help narrow it down.

My discord is Sinkoh

Added.

Changed Status from Pending to Closed

Changed Fixed In to Next Version